In the use, transfer and handling of purified or corrosive liquids including liquid chemicals it is desirable, and often essential to prevent contamination of the liquids by dirt, dust or other foreign substances. Such contamination may occur during the filling or emptying of containers or drums used to store or transport the liquids.
Others have disclosed a variety of closures for drums including valves or caps, some equipped with gates or discs with apertures, which may be alternately opened and closed by suitable mechanical means. Representative of such prior devices are those disclosed in U.S. Pat. Nos. 1,623,056 issued Apr. 5, 1927; 2,247,227 issued June 24, 1941; 2,254,268 issued Sept. 2, 1941; 2,736,339 issued Feb. 28, 1956; 2,832,561 issued Apr. 29, 1958; 2,858,847 issued Nov. 4, 1958; 2,878,829 issued Mar. 24, 1959; 2,889,852 issued June 9, 1959; 2,959,330 issued Nov. 8, 1960; 3,035,603 issued May 22, 1962; 3,434,498 issued Mar. 25, 1969; 3,498,313 issued Mar. 3, 1970; 3,519,014 issued July 7, 1970; 3,625,255 issued Dec. 7, 1971; 3,855,997 issued Dec. 24, 1974; 3,984,021 issued Oct. 5, 1976; 4,082,206 issued Apr. 4, 1978 and 4,224,958 issued Sept. 30, 1980. Many of these devices include complicated features such as spring valves and/or are not suitable for shipment with the containers because of possible damage in transit, or do not ensure contamination-free filling or transfer of the liquids into or from the containers.